Estimation of void volume in insulation system from partial discharge parallelogram measurements

A practical means of obtaining the geometrical capacitance increment between the solid insulation capacitance (with cavities short-circuited completely) and the low-voltage capacitance without discharges in an insulation system from parallelogram measurements has been used to estimate the fractional volume of voids in the insulation system. This method has been evaluated by tests on models and generator insulation. From a comparison between calculated results and those obtained from experiment, it is found that more accurate estimation can be made by using this geometrical capacitance increment. An attempt is made to estimate the void volume of HV generator stator insulation